1. Field of the Invention
The present invention relates to a heat pump type refrigerant cycle system which improves heating capacity by injecting middle-pressure gas refrigerant into a compressor. The refrigerant cycle system is suitably used for an electrical vehicle air conditioner, for example.
2. Description of Related Art
In a vehicle such as an electrical vehicle, because it is impossible to heat a passenger compartment by using engine-cooling water as a heating source, a heat pump type refrigerant cycle system is mounted on the vehicle, and the passenger compartment is heated by refrigerant-condensing heat in a condenser. However, when the refrigerant cycle system is used in an outside air temperature lower than -10.degree. C., heat-absorbing amount of refrigerant in an exterior heat exchanger used as an evaporator for heating operation is decreased, and pressure of refrigerant sucked into a compressor is decreased. Therefore, refrigerant specific volume sucked into the compressor is increased, and an amount of refrigerant circulating in the refrigerant cycle system is decreased. Consequently, there occurs a problem that heating capacity for the passenger compartment becomes insufficient.
To overcome the problem, in a refrigerant cycle system described in U.S. Pat. No. 5,704,219, high-pressure refrigerant is pressure-reduced to a middle pressure during the heating operation, the middle-pressure refrigerant is separated into gas refrigerant and liquid refrigerant in a gas-liquid separator, and the gas refrigerant having the middle pressure is injected into a compressor. Therefore, a compression amount of refrigerant in the compressor is increased in the heating operation, and the heating capacity for the passenger compartment is improved. Further, in the conventional refrigerant cycle system, an evaporator of the refrigerant cycle system is disposed on an upstream air side of an air passage of an air conditioning unit, and a condenser of the refrigerant cycle system is disposed in the air passage on a downstream air side from the evaporator, so that defrosting operation for defrosting a windshield is performed.
However, in the conventional refrigerant cycle system, during heating operation, the middle-pressure gas refrigerant separated in the gas-liquid separator is decompressed to a low pressure by a thermal expansion valve, and the low-pressure refrigerant is evaporated in the exterior heat exchanger, so that super-cooling degree of refrigerant sucked into the compressor is adjusted by the thermal expansion valve. Therefore, when the heating operation is performed with low load, a flow rate of refrigerant flowing into the exterior heat exchanger is decreased by decreasing a rotation speed of the compressor, and oil contained in refrigerant tends to stay in the exterior heat exchanger. As a result, an oil amount returning to the compressor is decreased.
On the other hand, a refrigerant flow in the refrigerant cycle system is switched by using a four-way valve disposed in a refrigerant discharge side of the compressor, so that gas refrigerant discharged from the compressor is introduced into the exterior heat exchanger during the cooling operation or is introduced into the interior condenser during the heating operation. Further, middle-pressure gas refrigerant is separated from liquid pressure in the gas-liquid separator before being injected into the compressor. Thus, refrigerant pipe structure of the refrigerant cycle system becomes complex, and component number thereof is increased.